Alternating-current transformer



oct. 9, 1923. 1,470,214

.L R. BR'uEcKNl-:n-

l ALTERNATING vCURRENT TRANSFORMER Fuel: Aug. 2 sheatslsieet 1 @manPatented Oct. 9, 1923.

UNITED STATES PATENT OFFICE.

JULIUS R. BRUECKNER, OF DETROIT, MICHIGAN, ASSIGNOR TO GIBBV INSTRUMENTCOMPANY, OF DETROIT, MICHIGAN, A CORPORATION OF PENNSYLVANIA.

ALTERNATING-CURRENT TRANSFOBMER.

Application med August 2a, 1920. seran ita-105,466.

To ill whom it may concern.'

Be it known that I, JULIUS R. Bannon- Nnn, a citizen of the UnitedStates, residing at Detroit, county of Wayne, State of Michigan, haveinvented a certain new and useful Improvement in Alternating-CurrentTrans'- formers; and declare the following to. be a full, clear, andexact description of the same, such as will enabe others skilledin theart to which it pertains to make and use the same, reference being hadto the accompanying drawingzjrs, which form a part of thisspecification. v

This invention relates to alternating current transformers for electricWelding systems. Electric arc Welding transformers have been devisedheretofore and in such previous cases, for instance as shown in the U.S. Patent for Morton Arendt, No. 1,146,988 of July Q0, 1915, aninductance or reactance coil is used in the secondary circuit or suchcircuit is provided with an in terwoven or' additional secondary windingas inthe U. S. Patent' to Claude J. Holslag i\o. 1,305,362 of June 3,1919, or an auxil- "iary secondary coil is' wound somewhere along themagnetic core which functions as a reactance or a choke coil.

All theseformer devices have a lare ohmic resistance-(since impedancemay looked upon in the same light as ohmic rev sistance) and theseformer types of transto negative is so slow that t e gas formed atformels are therefore of 10Wv eiciency. due` to excessive consumptlon ofpower Whlch 1sthe arc (which is thecurrent conducting element) has timeto dissipate making'such transformers unsuitable Afor arc weldingf Theintroduction of reactance' coils and the like as heretofore mentionedresults in a distortion of current flow to cause ra id drop in voltagethrough the zero va ue.

The curve'of the instantaneous values durmg this vcontinuous change frompositive yto negative is termed the "current or E. M. F. Wave form andfor all practical purposes maybe considered a. sine wave which isusually peaked or rounded at the top: By introduction of reaetance coilsin the secondary circuit as heretofore mentioned, the wave form may bechanged thus flattening out the top of the sine wavewith a sudden changefrom maximum lpositive to maxi- ,mum negative across the neutral points.

This distortion ofthe sinewave is a direct result of the difference inphase relation of the E. M. F. and current. Ifthis distortion is causedby reactance the current lags behind the E. M. F. `An object of thisinvention is to provide an alternating current electric arc weldin verysimple construction ispensing with or avoiding the use of' reactancecoils, or ad lditional magnetic by-paths, interwoven .or

split secondaries and in which the current loss is reduced to a minimum.Further, the object is te provide a construction :produc-tive of asteadyarc and an even stable flow of current across the arc anddistinguishes from the former devices above mentioned ink that theconstruction provides a definite means of producing a short and steadyarc by magnetic flux distortion rather than by direct current distortionas transformer of in the former cases. In other Words-the object of theinvention is to'provide a transformer having a core of such constructionand design as vto. induce a current in theV secondary in which thechange through the neutral point from maximum sitive to maximum'negative value is sud en instead of producing a secondary current ofsubstantially normal Wave form and introducing an Vinstrumentality inthe circuit to distort such wave formi as is the usual practice. Vith myinvention a current of the' desired character is primarily set up in thesecondary. character With which I am acquainted the induced current isacted upon to cause the sudden drop from maximum positive to maximumnegative value. These and other objects and lthe several novel featuresof the invention are hereinafter more fully described andclaimed and thepreferred form of construction 'of a transformer embody? With all otherdevices of this ing my invention is shown in the accompanying drawingsin which- "Fig: 1 is a side elevation ot' a transformer.

Fig. 2 is a detail of the mechanism for moving the secondary coil.

Fig. 3 is a plan view` of the transformer, taken on line 3-3 of Fig. l.Y y

I F ig. 4 is a diagram showing the wave form of the standard type oftransformer.

Fig. 5 is a diagram showing the ideal 'wave form of the secondarycurrent as approximately produced by the transformer here shown.

My improved transformer is ofthe usual shell type having three legs, 1,2 and 3. The primary coil i and the secondary coil 5 are two distinctunits each surrounding the center coreand the primary winding is,securely fastened at the lower end of the core 2. This fastening may beof any approved type as by bolts G passing through a frame 7 and basemember 8 of the trans'- former. The secondary winding 5 is movable onthe core 2 and by movement of the secondary coil the secondary currentmay be varied as heretofore described. lVhen the secondary isnearest/the primary the maximum secondary current is obtained and whenfurthest from the primary the minimum current is available. This movement of the secondary coil isaccomplished by meansof a rack 9 whichextends upward through the closed casing of the trans former and engagesa pinion 11 shown more particularly in Fig Z on the shaft of theoperating wheel 10. This movable secondary is essential for differentclasses ot' work requiring a greater or less degree of heat at the are.As the transformer is preferably enclosed within a casing 12 some meansshould be provided to enable the operator to determine the relativeposition of the secondary coil as for instance by placing graduationlines (not here shown) on the rack end 9.

The primary coil is provided with leads 13 and 14 while the secondarycoil is provided with the leads'll and'lG the lead 15 providing theground line and the line 16 being provided with an electrode holder 17.These several leads are connected with the respective tcoils in theusual manner being supported on the upper end of the trans former byinsulating block 18. The closed casing is lled with oil preferably toabout the upper end of the transformer so that both coils are immersedin the oil. I have found by a series of carefully conducted eX-periments that, by maintaining the core portions in certain .relation tothe winding of the primary and secondary and the length of the core indefinite proportion to the width of the windows of the transformeronder;7 windings or intermingling the pri mary and secondary or theaddition of a reactance coil or the like in the secondary circuit.Therefore, by the construction stated the impedance or ohinic resistanceof the windings is reduced to a minimum.

The relative proportions of the core parts that I have found mosteffective is in providing a window of three and one-half inches widthand fifteen inches in length with a two inch width of each outside legvand four inch width ot central leg. The capacity of transformers may bevaried by adding metal to the side thereof to increase the crosssectional area and cubical content of the core parts. This structurepermits the usel of a comparatively low voltage open circuit for t-hestriking of the arc greatly reducing the shock hazard and providing acore of sufficient capacity to permit the magnetic iux to surge withoutleakage when the transformer is on open circuit. The comparativelynarrow windows also provide a ready means for magnetic leakage when thetransformer is under load (that is when an arc is maintained). Byreducing the ohmic resista-nce to a minimuml (as by elimination of chokecoils etc.,) the current losses are reduced and at the Same time asteady and an even fiow of ciu-rent across the arc is secured. Thesebeneficial results are obtained through distortion of magnetic tiuxrather than by directly distorting the current as formerly and thetheory of operation is as follows: Vhen the secondary circuit is openand current passing through the primary, the magnetic field isunobstructed throughout the several parts of the core. Upon closing of.the secondary circuit, as in the striking of the arc, and with thesecondary spaced to some extent from the primary, there is what istermed a magnetic leakage between the central leg and outside legs ofthe core between lthe two coils, the extent of which is determined bythe spacing of the coils. Vhen t-he secondary circuit is closed, themagnetic flux may not take its normal path'due to the counteractinginfluence of that set up by the secondary coil at the upper end of thecore. The greater the distance between the secondary coil and theprimary coil the less will be the amperage and the greater the voltageof the secondary current and decreasing the distance between the coilsincreases the amperage and decreases the voltage.

It is well known in the art that a short arc is essential in theproduction of a good weld and that, due to oxidation, the weld isbrittle when a long arc is maintained. Vith the construction ofapparatus according to my invention the arc will extinguish uponlengthening to a dangerous point due to the comparatively low voltage ofthe secondary circuit and thus the length of the struction and design ofni Iao - velo are ossible to be drawn is automatically regu ated andmaintained within the necessa limits for the production of a good we d.For the usual arc welding operation, the secondary coil should bepositioned about midway between the'primary coil and up` vper end of thecore in the .design herein wave form isy secured and heretofore`deemed-necessary in securing the desired wave form. By the particularityof contransformer, especially the narrow win ows having va Widthpractically onefourth of the height, a ready leakage of magnetic flux isermitte-:l when the coils are separated, an I avoid the detrimentalfeatures of the former oonstruction mentioned and secure the followingdesired results--namely, low current consumption due to the currentimpedance being reduced to a minimum, a comparatively low voltage onstriking the yarc and, simply varying the position of the secondary,automatically varies the extent of magnetic leakage and varies thecharacter of the current to correspondingly vary the heat ded at thearc. e'benefits obtained by the construction heretofore set forthlresults principally from the use vof an excessive massA of iron inrelation to the mass of copperwith a comparatively veryshortf'iiiagnetic'air gap se- ,ciired by the narrow windowconstruction.`

As before stated, the central leg of the transformer has a width equal4to the two outside ylegs with the air space therebetween aboutone-fourth the height. The transformer is made of a series of plates sothat the length of the transformer may be increased or diminishedreadily by addition' or removal of one or more plates. In-thespecific-transformer heretofore mentioned having windows-of about threeand onehalf inches by fifteen inches I use approximately ninety-twoturns in the primary coil, using a at wire ..125 thick and .375 wide.The second coil is made of forty-four turns of two wires each of .125 by1440; With the construction I secure ninety volta in the secondarycircuit with 22() volts in the primary circuit. Thel'mass of iron weighsapproximatel 200 pounds, and the 'mass of copper Weig is approximatelypounds. 4With this construction the voltage in the secondary on opencircuit is ninety irrespective of the position of the secondary.laminated core' formed of three legs of mag- There is no variation inthe voltage that may be detected by any of the usual instruments whetherthe secondary is positioned adjacent the primar coil or at a point mostremote there rom. Thisl indicates positively that there is no magneticleakage whatever when the secondary is on open Vcircuit although, byreasonof the short air gap a very ready magnetic leakage occurs` onclosed circuit-as themagnetic flux of the primary is counteracted bythat of the secondary. The essential characteristic of my' inventionconsists in the provision of en excessive mass of iron relative to thecopper as compared with that of the standardalternatingcurrent type oftransformer and in so constructing thetransformer .to permit a highdegree of magnetic leakage to readil shorten the path of the magneticcircuit o the primary coil. In this manner,

when the secondary circuit is closed, as upon striking an arc, adistortion of the magnetic fiux of the primary coil is occasioned and,

as this is out of phase with that set up by the secondary on closedcircuit, a prolonga- .tion of the maximum, positive and max- 'imi'imnegative value sof the secondary current is occasioned together with asudden Adrop therebetween through the neutral fpoint. This is a desiredwave form of secondary current as heretofore stated and by theconstruction described, a current of the desired wave form is primarilyeffected in the secondar circuit rather than secondarily eiecte throughthe introduction in the secondary circuit of a reactaiice coil or the'like as has been the practice. The specific proportions of thetransformer parts herein specified are iven `solely as an example and itis to e understood various changes may be within the limitations of theappended claims without departing from the spirit of the invention.Having thus fully described my invention, whatfI claim and desire tosecure by Letters Patent of the United States is- 1. Air alternating'vcurrent transformer for use in electric are weldin comprising a coreformed with three legsI 0% magnetic'ma-A terial connected together atthe top and bottom, the windows'between the legs being of a-widthvsubstantially one fourth their length roviding a short air gap, aprimary circuit aving a coil at the bottom of the ycentral leg, asecondaryhcircuit, -a movable `-coil therein on the central .leg abovethe primary coil, means for holding the secondary coil at any of itspossible distances from the primary, the secondary coil and circuit beinyfree' from ohmicresistance other than that inherentin the wire formingthe same andthe resistance of the arc.-

2. An alternating current transformer for use in electric arc weldingcomprising a liao netic material connected together at the top andbottom and having narrow window-S between the legs providing a shortmagnetic air gap permitting ready magnetic leakage, a prima'ry circuithaving a. coil at the bottom ot the central leg, the mass ot iron beingsutiicient to permit surge of magnetic flux without leakage, a secondarycircuit having a coil on the central leg adapted to be adjusted tovarious delinite positions relative to the primary, the secondary coiland circuit being unimpeded except by the inherent resistance of thewire and the resistance of the arc.

3. An alternating ciiirent transformer for use in electric are weldingcomprising a core formed of three legs of magnetic material connectedtogether at the top and bottom, the width of the central leg beingsubstantially equal to that of both the other legs and the three legsbeing connected together at the top and bottom, the windows between thelegs being comparatively narrow and of the same Width throughout theirlength and providing a comparatively short magnetic air gap permittingready magnetic leakage,'a primary circuit having a coil on .the core, asecondary circuit also having a coil on the core, means whereby one ofthe coils may be positioned and held, the iow of current through eitherof the circuits and respective coils being impeded only by the naturalresistance of the Wire form-v ing said circuits and the resistance ofthe arc in the secondary circuit.

4. An alternating current for use in electric arc Welding whichcomprises a core formed of three legs of magnetic material connectedtogether at the top and between and providing windows7 between the legsof a uniform width of about one-fourth their length providing a shortmagnetic air gap and whereby the extent of magnetic leakage 1sproportioned to a distance the coils are positioned apart. a primarycircuit having a coil fixed at the bottom ct the central leg, asecondary circuit free from impedance except that natural to the wire ofthe circuit and the resistance of the arc and having a coil about thecentral leg and movable thereon relative to the primary, and means forpositioning the secondary and holding the saine at various predetermineddistances from the primary, coil whereby the an'iperage of the secondarycircuit is determinable.

5. An alternating current transformer for use in electric arc weldingcomprising a core having a cross sectional area sullcient to normallypermit unrestricted magnetic linx, said core further having a formpermitting a high degree of magnetic leakage, a primary coil and circuittherefor of a character permitting practically unimpeded flow ofcurrent, a secondary circuit free from impedance except that natural tothe wire and the resistance of the arc and having a coilniovablerrtoward Vor from the primary coil to effect magnetic leakage bydistorting the magnetic flux of the primary coil to a desired extent,the said secondary coil and circuit therefor, by reason of the freedomof magnetic leakage and ,unrestricted magnetic flux having currentprimarily induced therein of a wave form having prolonged maximumpositive and maximum negative values with a sudden drop through theneutral point therebetween.

In testimony whereof, I sign this specification.

JULIUS R. BRUECKNER.

